The Protein Phosphatase Activity of PTEN Regulates Src Family Kinases and Controls Glioma Migration

Abstract

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is mutated or lost in 60% to 70% of advanced gliomas and is associated with malignant phenotypic changes such as migration, which contribute to the morbidity and mortality of this disease. Most of the tumor suppressor function of PTEN has been attributed to its ability to dephosphorylate the second messenger, phosphatidylinositol 3,4,5-triphosphate, resulting in the biological control of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. Despite recent work suggesting that the protein phosphatase activity of PTEN controls glioma cell migration, the mechanisms by which this occurs are unclear. Herein, we show using glioma cell lines (U87MG and U373MG) stably transfected with wildtype PTEN or catalytically altered mutants of PTEN that PTEN controls integrin-directed migration in a lipid phosphatase, PI3K/AKT-independent manner. Confirming this observation, we show that the stable overexpression of COOH-terminal Src kinase, the physiologic negative regulator of SRC family kinases (SFK), or treatment with the SFK inhibitor PP1 abrogates glioma migration. The results provide direct evidence that the downstream effect of the protein phosphatase activity of PTEN is to suppress SFK and FYN, and to regulate RAC-GTPase activity after A v integrin stimulation. Furthermore, studying vitronectin-directed migration using (a) Fyn small interfering RNA and (b) astrocytes from Fyn heterozygous (+/À) mice, Pten heterozygous (+/À) mice, Pten and Fyn double heterozygous (+/À) mice, or Fyn knockout (À/À) mice confirmed a role of FYN in A v integrin-mediated haptotaxis in glial cells. Our combined results provide direct biochemical and genetic evidence that PTEN's protein phosphatase activity controls FYN kinase function in glioma cells and regulates migration in a PI3K/AKT-independent manner.

Resistance to EGF receptor inhibitors in glioblastoma mediated by phosphorylation of the PTEN tumor suppressor at tyrosine 240

“…This activity is associated with inhibition of invasion in glioma cells and more recently has been shown to increase sensitivity to ErbB2 inhibition by trastuzumab in breast cancer cells (2,39), but it is unclear as to which signals may determine the outcome of the PTEN-SFK interaction. By invoking FGFR as an additional input into PTEN phosphorylation, our data may help to explain how this reciprocal interaction can be regulated.…”

“…In recent years it has become clear that PTEN also performs a number of tumor suppressor functions independent of its lipid phosphatase activity, including the suppression of cell migration, maintenance of genomic stability, and inhibition of cell cycle progression (2)(3)(4)(5). The PTEN gene is lost or mutated in ∼40% of glioblastoma multiforme (GBM) (6,7), and retention of PTEN protein expression has been linked with responses to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in GBM patients (8,9), suggesting that the detection of functional PTEN may inform the successful deployment of targeted therapeutics in this currently intractable disease.…”

The role of the PI3K/AKT/mTOR pathway in brain tumor metastasis

“…[92] PTEN controls integrin-dependent migration through the regulation of Src family kinase activation, in a PI3K/AKT-independent manner. [93] The re-expression of PTEN in GBM cell lines increases the cellular content and activity of the p53 tumor suppressor protein inducing cell cycle arrest and increasing the sensitivity of the tumor cells to various chemotherapeutic agents such as etoposide. [94] Upstream regulators of EMT induction, such as insulin-like growth Factor-1 receptor (IGF-1R), c-MET and the CXCR4 receptor, have been proposed as potential targets to inhibit GBM or MB invasion.…”

PTEN signaling in brain: neuropathology and tumorigenesis

“…It is possible that the effects of PTEN on cell migration in vitro are dependent on experimental conditions. Indeed, studies suggesting that the lipid phosphatase activity of PTEN regulates migration by RAC1 inhibition were performed on fibronectin and mediated by a 5 b 1 integrin (Liliental et al, 2000); however, Dey et al (2008) studied glioma cell migration on vitronectin, which binds a v b 3 integrin, and showed that PTEN's protein phosphatase activity negatively regulated RAC1 indirectly by regulating the activity of the SRC-family kinase, FYN. It has also been suggested that PTEN may regulate cell migration by directly dephosphorylating FAK in the DBTRG-05MG glioblastoma cell line (Tamura et al, 1998); however, other studies have shown that PTEN does not influence FAK phosphorylation in other cell lines (Maier et al, 1999;Jones et al, 2001).…”